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| | IN-VITRO FLUORESCENCE ASSAY |
| Description: | In order to identify modulators of cathepsin D activity, a continuous enzymatic test was carried out with a synthetic peptide which carries a fluorescent group (MCA=(7-methoxycoumarin-4-yl)acetyl) which is quenched by energy transfer from a Dpn (2,4 dinitrophenyl) group on the same molecule, in Greiner 384-well nb microtitre plates. Cleavage of the peptidic substrate by cathepsin D causes an increase in the fluorescence intensity. In order to determine the efficacy of substances, the time-dependent increase in the fluorescence intensity in the presence of the substance was compared with the time-dependent increase in fluorescence in the absence of substances. The reference substance used was pepstatin A (Sigma-Aldrich). The substrate used was MCA-GKPILFFRLK(Dnp)d-R—NH2 (Enzo Life Sciences, L rach). The enzyme employed was cathepsin D isolated from the human liver (Sigma-Aldrich) in a final concentration of 1.4 nM. The test was carried out in 100 mM sodium acetate buffer, 1.25% (v/v) of DMSO, 0.25% (w/v) of Chaps, pH 5.5. 2 μl of each substance solution with serially diluted substance concentration were added to in each case 4 μl of cathepsin D solution and incubated at room temperature for 10 min. The reaction was started by addition of 2 μl of substrate solution (final concentration 5 μM). After carrying out a starting-point fluorescence measurement (excitation wavelength 340 nm/emission wavelength 450 nm) using an Envision multilabel reader (Perkin Elmer), the reaction was incubated at room temperature for 60 min. The amount of peptide fragment cleaved off during the reaction time was subsequently measured by determination of the increase in the fluorescence intensity at 450 nm (excitation wavelength 340 nm). |
| Affinity data for this assay | |
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